In addition to a normal combustion chamber called a main chamber, a precombustion-chamber type lean premixed gas internal combustion engine (hereinafter, referred to in short as a “gas engine”) includes a combustion chamber communicating with the main chamber via a nozzle, which is referred to as a precombustion chamber.
An intake valve is opened during an intake stroke to introduce lean mixed gas into the main chamber and combustion gas into the precombustion chamber, and mixed gas is produced by mixing the lean mixed gas that flowed into the precombustion chamber from the main chamber via the nozzle during a compression stroke and the fuel gas supplied to the precombustion chamber during the intake stroke.
The produced mixed gas is combusted by an ignition spark of a spark plug disposed in the precombustion chamber, and a flame is injected into the lean mixed gas in the main combustion chamber from the precombustion chamber via the nozzle.
This flame is injected into the lean mixed gas in the main combustion chamber to perform main combustion.
According to Patent Document 1, an engine includes a main chamber facing a piston and a precombustion chamber communicating with the main chamber via a nozzle as combustion chambers. The engine further includes a precombustion-chamber fuel supply channel for supplying fuel gas to the precombustion chamber and the first check valve which is disposed in the precombustion-chamber fuel supply channel and which opens due to a pressure decrease in the precombustion chamber to allow supply of fuel gas to the precombustion chamber.
A branch channel is formed on the precombustion-chamber fuel supply channel between the first check valve and the precombustion chamber at an end portion on a downstream side. The branch channel includes the second check valve which opens due to a pressure increase in the precombustion chamber to allow gas to flow in from the precombustion-chamber fuel supply channel.
With the above structure, the first check valve opens while the second check valve is maintained to be closed upon a pressure decrease in the precombustion chamber. Thus, it is possible to supply fuel gas to the precombustion chamber.
When a pressure in the precombustion chamber increases, the second check valve opens while the first check valve is maintained to be closed. Thus, the fuel gas having been prevailing in the precombustion-chamber fuel supply channel at the downstream side of the first check valve flows into the branch channel.
In this way, when ignition takes place in the precombustion chamber and the mixed air is combusted, the pressure in the precombustion chamber increases and the second check valve opens.
As a result, the combusted gas in the precombustion chamber flows into the precombustion-chamber fuel supply channel, and the non-combusted gas having been compressed in the precombustion-chamber fuel supply channel flows into the branch channel. Thus, the precombustion-chamber fuel supply channel between the first check valve and the precombustion chamber is filled with the combusted gas. In an expansion stroke, a pressure in the precombustion chamber decreases due to descent of the piston and the second check valve closes, so that the gas in the precombustion-chamber fuel supply channel at the downstream side of the first check valve gradually flows out into the combustion chamber. Here, the precombustion-chamber fuel supply channel at the downstream side of the first check valve is filled with the combusted gas, which makes it possible to prevent non-combusted gas from flowing out into the combustion chamber.
Accordingly, Patent Document 1 discloses reducing the amount of discharge of non-combusted gas in the next exhaust stroke after the expansion stroke to improve engine efficiency.